Sleep Basics

Sleep is a physical and mental resting state in which a person becomes relatively inactive and unaware of the environment.

Normal sleep is characterized by a decrease in body temperature, blood pressure, breathing rate and most other body functions but the brain remains active.

Wakefulness is a state of awareness in which the individual is conscious of his/her surrounding environment and is able to react with it.

Sleep Cycle

Sleep is characterized by two distinct states, non-REM sleep and REM sleep that alternate in 90 to 110-minute cycles.A normal sleep pattern has 4-5 cycles throughout the night.

The stages of sleep are determined with a polysomnogram (PSG) or sleep study. The PSG records vital signs and physiology during sleep including:

• Electro-encephalogram (EEG)
• Electro-myograph (EMG)
• Electro-oculograph (EOG)
• Respiratory airflow
• Blood oxygen saturation
• Pulse rate
• Heart rate
• Body position
• Respiratory effort

Non-REM sleep consists of four stages that range from light dozing to deep sleep. Approximately 75% of night's sleep is spent in non-REM sleep.

Stage 1 Sleep is a transition period from wakefulness to sleep. It is characterized by slow rolling eye movements. The dozing stage. Approximately 5% of the the total night's sleep is spent in Stage 1.

Stage 2 Sleep is characterized by a lack of eye movements. Brain waves become larger.It is defined on PSG with sleep spindles and K-complexes. Approximately 45% of the total night's sleep time is spent in Stage 2 of non-REM sleep. This stage is often considered the official onset of consolidated sleep. Eye movements stop and brain waves become larger.

Stage 2 Sleep is graphically defined with two distinct brain wave forms called sleep spindles and K-complexes. A sleep spindle is a pattern of EEG waves, consisting of a burst of 11 to 15 hertz waves that last for .5 to 1.5 seconds. A K-complex is high voltage EEG activity that consists of a sharp downward component followed by a slower upward component and lasts more than .5 second.

In Stage 3 sleep, an individual becomes difficult to arouse. On the PSG, large and slow delta waves appear. Approximately 12% of the total night's sleep time is spent in Stage 3 of non-REM sleep.

Stage 4 Sleep is characterized by very deep sleep. When awakened, person feels groggy and disoriented.PSG shows delta waves almost exclusively. Approximately 13% of the total night's sleep time is spent in Stage 4 of non-REM sleep.

REM Sleep

Most dreaming takes place during REM sleep. REM sleep makes up about 20  25% of the sleep cycle in normal adults. REM sleep is characterized by:

• Eyelid fluttering
• Rapid eye movement
• Muscle paralysis
• Irregular breathing
• Decrease in body temperature
• Changes in heart rate and blood pressure

Normal Breathing

When you breathe normally, air passes through the nose and past the flexible structures in the back of the throat such as the soft palate, uvula and tongue. While you are awake, muscles hold the airway open. When you fall asleep, these muscles relax but, normally, the airway stays open. In people with sleep apnea, the airway collapses during sleep.

Snoring

Snoring is the sound of obstructed breathing during sleep. While snoring can be harmless (benign snoring), it can also be the sign of a more serious medical condition which progresses from upper airway resistance syndrome (UARS) to obstructive sleep apnea (OSA).

What causes snoring?

Snoring occurs when the structures in the throat are large and when the muscles relax enough to cause the airway to narrow and partially obstruct the flow of air. As air tries to passes through these obstructions, the throat structures vibrate causing the sound we know as snoring. Large tonsils, a long soft palate and uvula and excess fat deposits contribute to soft tissue narrowing.

Obstructive Sleep Apnea

When obstructive sleep apnea occurs, the tongue is sucked against the back of the throat. This blocks the upper airway and air flow stops. When the oxygen level in the brain becomes low enough, the sleeper partially awakens, the obstruction in the throat clears and the flow of air starts again, usually with a loud gasp.

People with obstructive sleep apnea (OSA) have disrupted sleep, and low blood oxygen levels. OSA has been associated with cardiovascular problems and excessive daytime sleepiness. The condition known as upper airway resistance syndrome (UARS) lies midway between benign snoring and true obstructive sleep apnea. People with UARS suffer many of the symptoms of OSA but sleep testing will be negative.

How do you know if you have OSA?

Take a simple test but be sure to visit your physician if you think you have a problem. This test is for daytime sleepiness not specifically for snoring and apnea.  If you score high on the test be sure to visit your physician or dentist.